1. Field of the Invention
Embodiments in accordance with the present invention relate to methods and systems for sensor data reporting with high positional accuracy and low power consumption.
2. Description of Related Art
Automatic wireless monitoring is prevalent in a variety of industries where location and other characteristics of a product or environment must be closely monitored for safety or regulatory reasons, such as hospitals. Other environmental parameters may also be important due to the nature of what items or processes (e.g., manufacturing processes) are being monitored. For example, humidity, exposure to light, motion sensors, positional location within a predetermined area, orientation of the product (e.g., whether or not it is upright), etc. may be important.
In many such places a facility is already wired with a communication infrastructure, particularly a Wi-Fi infrastructure, and wireless monitoring is achieved by connecting appropriate sensors with small Wi-Fi transceivers (i.e., tags) that can transmit the measured parameter(s) to a central server, which in turn distributes the measurements to applications that need to monitor the parameters. Although standard Wi-Fi provides bi-directional communication, standard Wi-Fi uses power relatively inefficiently. Consequently, a battery-operated standard Wi-Fi transceiver must use large and/or heavy batteries, or the batteries must be replaced relatively frequently. A variation of the Wi-Fi protocol that uses one directional communication from the tag to the Access Points is used by a few Wi-Fi infrastructure providers. This protocol is much more power efficient as it does not require association between the tags and the Access Points for communication. An example of such a protocol is the CCX protocol that, while using the Wi-Fi Physical layer and MAC structure, is not a conventional Wi-Fi packet that is IP based and as such requires 2-D communication between the Access Points (AP) and the tags. Other one-directional systems such as Aruba™ are also known.
Indoor Real-Time Location Systems (“RTLS”) have gained popularity and are a mainstream product now. RTLS is especially popular in the healthcare industry for a variety of applications ranging from asset tracking through patient and staff tracking, environmental or patient sensing (e.g., temperature), hygiene compliance, elopement (i.e., a patient leaving a facility without authorization), theft prevention, and so forth.
Major drawbacks of using conventional Wi-Fi-based RTLS technology include:
First, tags (i.e., the mobile portion of the system) use relatively high power consumption. The high power consumption is inherent to Wi-Fi technology because Wi-Fi is ordinarily targeted for high-bandwidth applications. Support in conventional Wi-Fi for large bandwidth results in peak and average power requirements that are much larger than competing 900 MHz and 433 MHz technologies.
Second, although usage of one-directional CCX tag transmission helped reduce somewhat the power consumption, with CCX there is no back channel from the server to the Wi-Fi tags. Lack of a back channel prevents realization of benefits arising from being able to communicate back to the tag for network-type information that would allow the tag better utilize its resources as well as possible parameters changes. Although bi-directional communication may be implemented by assigning Internet Protocol (“IP”) addresses to the tags and using standard Wi-Fi protocols, such an implementation is known to be highly power consuming.
Cisco™ Compatible Extensions (“CCX”) are a vendor-developed standard designed and promulgated for Cisco Wi-Fi networks. A CCX-based system is used in Cisco Wi-Fi-based Real-Time Location Systems (“RTLS”). A CCX-compatible tag transmits one-directional packets with a flexible format that is recognized by Access Points (“APs”) using a predefined header. The APs transmit the packet with other support information, such as a received signal strength indicator (“RSSI”), to a Cisco mobility services engine (“MSE”) that uses the information from multiple APs to calculate location using triangulation. A CCX-based system presents an advantage over the standard bi-directional Wi-Fi communication because, first, the CCX-based system does not require for the tag to have an IP address. Second, one-directional communication substantially reduces power consumption by the tag.
Although a CCX-based system is adequate to support position location using triangulation methods, it is not adequate by itself to support position location methods having greater positional accuracy, such as those used in new generations of RTLS systems.
However, a first problem with using new generations of RTLS technology with a CCX-based system is tag power consumption. New generations of RTLS systems utilize secondary technologies such as infrared (“IR”), low-frequency RF (“LF”) or ultrasound (“US”). The secondary technologies are needed to provide a higher level of positional resolution that cannot be provided by triangulation alone. However, the secondary technologies consume additional power from the tags, thereby further burdening conventional Wi-Fi tags that already suffer from relatively poor power consumption.
One way to make the secondary technologies on the tag consume less power is through the use of synchronization, as disclosed in U.S. Pat. No. 8,139,945 (“the '945 Patent”), the entire content of which is hereby incorporated by reference in its entirety. Improved synchronization allows a tag to activate certain circuitry only when it may be needed. In the '945 Patent, in order to synchronize the end devices (i.e., tags and exciters), there must be a return link back from the system (e.g., an AP) to the end devices. The conventional CCX protocol is incapable of supporting the return link because the CCX protocol is one-directional.
A second problem arising from the lack of backward channel in CCX-based system is an inability to gain important performance enhancement to the RTLS resolution. One such enhancement is the use of virtual walls (“VWs”) as disclosed in U.S. Pat. No. 8,018,584 (“the '584 Patent”), the entire content of which is hereby incorporated by reference in its entirety.
Therefore, a need exists to substantially reduce the power consumption of Wi-Fi based tags and to help substantially improve the system positional accuracy, in particular the system positional accuracy when used in conjunction with secondary technologies such as Infrared, LF and/or Ultrasound.